The aim of this project is to elucidate the neuronal (CNS) mechanisms that mediate the effects of several hallucinogens (psychotomimetics) and other, related compounds. To this end, a sensitive, specific, robust and reliable "behavioral asset" in which rats or pigeons are trained to detect (discriminate) drug-induced alterations in their own internal environments (states), will be used to study several clinically-important ergot alkaloids including lergotrile and dihydro-ergotoxine (Hydergine). These compounds have been used to treat a variety of cardiovascular, neuroendocrine and neuropsychiatric disorders ranging from migraine headache to Parkinsonism and senile dementia. Special attention will be paid to (1) the extent to which the discriminable effects of therapeutic ergots resemble those of their close structural congener lysergic acid diethylamide (LSD) and therefore might predict hallucinogenic or psychotominetic liability; (2) the neuronal mechanisms underlying ergot cues; (3) possible correlations between the discriminable and (other) physiological and neurochemical effects of ergots.